Wristwatches driven by small size batteries installed therein have come into wide use as well as quartz timepieces using quartz crystal vibrators as time standards. A drawback inherent in this type of wristwatches resides in that the lifetime of such batteries is not more than 1-2 years requiring frequent replacement of batteries. To cope with this problem, there has been proposed a timepiece furnished with solar cells which convert solar energy into electric energy to charge the battery. Such a timepiece therefore needs no replacement of the battery.
However, a solar powered timepiece generally has an intricate construction because it includes a solar cell unit made up of solar cells, a diode for preventing reverse current, an overcharge preventing resistor, etc., in addition to the various component parts usually installed in a timepiece.
A simpler construction for a solar cell wristwatch may be obtained by forming the solar cells, diode, resistor and like components separately from the conventional movement of a timepiece. This however involves difficulty in the electrical connection between the movement and the solar cell unit, and assemblage thereof.
A further problem is that, among the components of the unit, at least the solar cells must be mounted with high accuracy since they will show themselves through a glass face plate of the timepiece.
Another problem arises from the fact that conventional wristwatches with solar cells may be generally classified into the following two types:
(A) A wristwatch having the solar cell unit positioned on a conventional wristwatch structure.
(B) A wristwatch whose movement has been designed to accommodate the solar cell unit.
The first type (A) of wristwatch is not acceptable from the viewpoint of design because the overall thickness of the solar cell unit and conventional movement is considerable. The second type (B) of wristwatch is effective when used solely as a solar cell wristwatch but has the following drawback where it is intended selectively to serve as solar cell wristwatch or an ordinary wristwatch. As an ordinary wristwatch, the wristwatch (B) has a structure designed to accommodate a solar cell unit, and the absence of the components of the unit results in unnecessary waste space and intricacy of arrangement.